U.S. patent number 5,360,044 [Application Number 08/078,111] was granted by the patent office on 1994-11-01 for pneumatic radial tire with high cornering and steering stability.
This patent grant is currently assigned to Sumitomo Rubber Industries, Ltd.. Invention is credited to Kazuo Asano, Akira Kajikawa, Kenji Saito.
United States Patent |
5,360,044 |
Saito , et al. |
November 1, 1994 |
Pneumatic radial tire with high cornering and steering
stability
Abstract
A pneumatic radial tire has a tread surface extending along a
specific curvature plane which includes a first arc with the radius
R1 having a center on the tire's equatorial plane and passing
through the tire's equatorial point, a second arc with the radius
R2 having a center on the tire's equatorial plane and intersecting
with the first arc at an intersection distant from the tire's
equatorial plane by 0.2 to 0.25 times the tire width SW, and a
third arc with the radius R3 passing through a ground contact outer
edge point of the ground contact surface, when a standard load is
applied, and a belt intermediate height point on the tread surface.
In the specific curvature plane, the curvature radius ratio R2/R3
is set in a range from 4 to 12, and the curvature radius ratio
R1/R2 is set in a range from 1.2 to less than 1.6 when the aspect
ratio H/SW is 0.70 or more. The tread surface is provided with a
main circumferential groove, preferably having a groove width of
0.06 to 0.10 times the tire width SW, extending near the
intersection of the first arc and the second arc in the tire
circumferential direction for dividing the tread surface into the
crown part and an outer shoulder part. Narrow lateral grooves
crossing the tire circumferential direction divide the crown part
and shoulder part into blocks.
Inventors: |
Saito; Kenji (Kobe,
JP), Kajikawa; Akira (Kobe, JP), Asano;
Kazuo (Kobe, JP) |
Assignee: |
Sumitomo Rubber Industries,
Ltd. (Kobe, JP)
|
Family
ID: |
26550218 |
Appl.
No.: |
08/078,111 |
Filed: |
June 18, 1993 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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964034 |
Oct 21, 1992 |
5277235 |
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598390 |
Oct 18, 1990 |
5222537 |
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Foreign Application Priority Data
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Oct 19, 1989 [JP] |
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1-272460 |
Dec 29, 1989 [JP] |
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1-341264 |
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Current U.S.
Class: |
152/209.14;
152/209.26; 152/209.27; 152/454; 152/538 |
Current CPC
Class: |
B60C
11/00 (20130101); B60C 11/0083 (20130101); B60C
11/0332 (20130101); B60C 11/11 (20130101); B60C
11/13 (20130101); Y10S 152/902 (20130101) |
Current International
Class: |
B60C
11/11 (20060101); B60C 11/13 (20060101); B60C
11/00 (20060101); B60C 003/00 (); B60C
011/00 () |
Field of
Search: |
;152/29R,29D,454,538 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0331453 |
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Sep 1989 |
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EP |
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2304487 |
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Oct 1976 |
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FR |
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0211404 |
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Jan 1990 |
|
JP |
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2198996 |
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Jun 1988 |
|
GB |
|
Other References
PCT document WO89/00113, Jan. 12, 1989, Asano et al..
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Primary Examiner: Ball; Michael
Assistant Examiner: Johnstone; Adrienne C.
Parent Case Text
This application is a divisional of copending application Ser. No.
07/964,034, filed on Oct. 21, 1992, now U.S. Pat. No. 5,277,235,
which is a divisional application of Ser. No. 07/598,390 filed on
Oct. 18, 1990, now U.S. Pat. No. 3,222,537 the entire contents of
which are hereby incorporated by reference.
Claims
What is claimed is:
1. A pneumatic tire comprising a carcass in radial structure
extending from a tread part through side wall parts and folded at
each edge around a bead core of a bead part, and a belt layer
composed of two belt plies disposed radially outside said carcass,
said belt layer having a pair of axial outer edges, each of said
pair of axial outer edges being defined where the two belt plies
overlap, wherein;
a tread surface is formed along a specific curvature plane which
includes
a first arc with the curvature radius R1 having a center on the
tire's equatorial plane and passing through the tire's equatorial
point,
a second arc with the curvature radius R2 having a center on the
tire's equatorial plane and intersecting with said first arc at an
intersection distant from the tire's equatorial plane by 0.2 to
0.25 times the tire width SW, and
a third arc with the curvature radius R3 passing through a ground
contact outer edge point of the ground contact surface in the axial
direction of a tire when a standard load is applied and a belt
intermediate height point on the tread surface,
said belt intermediate height point on the tread surface being
defined as a point at which a tire axial direction line crosses the
tread surface extending in parallel with the tire's axis from a
thickness center of one of said pair of axial outer edges; and
the tread surface is provided with a pair of main circumferential
grooves, one of said main circumferential grooves extending on each
side of the tire's equatorial plane at said intersection of the
first arc and the second arc in the tire circumferential direction
for dividing the tread surface into a crown part and an outer
shoulder part, each said main circumferential groove having a
groove width of 0.06 to 0.10 times the tire width SW, and with a
plurality of narrow lateral grooves crossing the tire
circumferential direction for dividing the crown part and the
shoulder parts into a plurality of blocks, wherein
the specific curvature plane has a curvature radius ratio R2/R3 in
a range from 4 to 12, and a curvature radius ratio R1/R2 in a range
from 1.2 to less than 1.6 when the aspect ratio H/SW of the tire
sectional height H to the tire width SW is 0.70 or more.
2. The pneumatic radial tire according to claim 1, wherein the
crown part or the shoulder part has a subsidiary circumferential
groove extending in the tire circumferential direction, with a
groove width of 0.1 to 0.3 times the groove width of said main
circumferential groove.
Description
FIELD OF THE INVENTION
The present invention relates to a pneumatic radial tire improved
in the cornering characteristic.
BACKGROUND OF THE INVENTION
Along with the recent trend of higher speed and higher performance
of vehicles, the tires are required to have improved steering
stability, especially, the straight-forward stability in high speed
running, gripping performance and break-away controllability in
cornering, both on dry and wet road surfaces. And accordingly,
hitherto, the double crown radius profile has been selected as the
tread surface contour.
In the conventional double crown radial tire, however, although the
steering wheel response and road surface gripping performance are
somewhat enhanced when running straight or at the initial moment of
turning, the limit performance in cornering, for example, breakaway
controllability, is not improved sufficiently.
The breakaway, in this case, refers to a phenomenon that the tire
skids and escapes from the cornering locus as the cornering force
generated on the ground contact surface becomes insufficient
against the centrifugal force by the slip angle of cornering. And
this is considered to occur, as shown in FIG. 8, when the cornering
force CF which has been increased approximately in proportion to
the slip angle .alpha. in the small slip angle range decreases its
increasing rate gradually in the large slip angle range.
SUMMARY OF THE INVENTION
It is hence a primary object of the invention to present a
pneumatic radial tire capable of improving the limit performance
when cornering, especially enhancing the steering stability in high
speed running, by basically forming a main groove of a broad width
near the intersection of the first arc and second arc while
defining the tread contour profile.
According to one aspect of the present invention, a pneumatic tire
comprises a carcass in radial structure extending from a tread part
through side wall parts and folded at each edge around a bead core
of a bead part, and belt layer composed of belt plies disposed
radially outside said carcass, wherein a tread surface is formed
along a specific curvature plane. The specific curvature plane
includes a first arc with the radius R1 of curvature having a
center on the tire's equatorial plane and passing through the
tire's equatorial point, a second arc with the radius R2 of
curvature having a center on the tire's equatorial plane and
intersecting with said first arc at an intersection distant from
the tire's equatorial plane by 0.2 to 0.25 times the tire width SW,
and a third arc with the radius R3 of curvature passing through a
ground contact outer edge point of the ground contact surface in
the axial direction of a tire, when a standard load is applied, and
a belt intermediate height point on the tread surface. The belt
intermediate height point on the tread surface is defined as a
point at which a tire axial direction line extending in parallel
with the tire's axis from a thickness center of the belt layer at
the axial outer edge of a region where at least two belt plies
overlap crosses the tread surface. Further, the tread surface is
provided with a main circumferential groove extending near said
intersection of the first arc and the second arc in the tire
circumferential direction for dividing the tread surface into the
crown part and its outer shoulder parts.
Preferably, the main circumferential groove has a groove width of
0.06 to 0.10 times the tire width SW, and narrow lateral grooves
crossing the tire circumferential direction for dividing the crown
part and shoulder part into blocks to divide the tread into the
crown part and the shoulder part. The crown part or shoulder part
may have a subsidiary circumferential groove extending in the tire
circumferential direction, with a groove width of 0.1 to 0.3 times
of the groove width of the main circumferential groove. On the
other hand, in the specific curvature plane, a curvature radius
ratio R2/R3 is set in a range from 4 to 12, and a curvature radius
ratio R1/R2 is set in a range from 2.6 to 4.6 when the aspect ratio
is 0.55 or less. Furthermore, a curvature radius ratio R1/R2 is set
in a range from 1.6 to less than 2.6 when the aspect ratio is more
than 0.55 and less than 0.70, and a curvature radius ratio R1/R2 is
set in a range from 1.2 to less than 1.6 when the aspect ratio is
0.70 or more.
The tread surface is formed along the specific curvature plane
having the first arc, second arc and third arc. Therefore, while
improving the ground contract surface shape, in addition to the
straight-forward stability in high speed running, the breakout
controllability in cornering is enhanced, and the turning stability
is improved.
Near the intersection of the first arc and second arc, there is a
wide main circumferential groove with the groove width of 0.6 to
0.10 times the tire width SW. Therefore, disturbance of ground
contact likely to occur at the intersection of arcs is eliminated,
and the cornering force is increased to improve the water draining
and ground contacting performances, thereby enhancing the wet brake
performance. The crown part and shoulder part having blocks divided
by lateral grooves increase the gripping force with the road
surface so as to improve the running performance.
BRIEF DESCRIPTION OF THE DRAWINGS
An embodiment of the present invention will now be described, by
way of example, referring to the attached diagrammatic drawings, in
which:
FIG. 1 is a sectional view showing an embodiment of the
invention,
FIG. 2 is a partial flat view showing the tread groove,
FIG. 3 is a diagram showing the contour profile of the tread
surface,
FIG. 4 is a diagram showing the specific curvature plane,
FIG. 5(a) to (e) are schematic drawings showing the ground contact
surface shape,
FIG. 6 is a schematic drawing showing the ground contact surface
shape when turning,
FIG. 7(a) is a diagram showing the relation between radius ratio
R2/R3 and ground contact width,
FIG. 7(b) is a diagram showing the relation between the radius
ratio R2/R3 and breakaway controllability, and
FIG. 8 is a diagram showing the relation between The cornering
force and slip angle.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an embodiment of the invention in the standard
internal pressure state, mounted on a standard rim 8 and inflated
with a standard internal pressure.
A pneumatic radial tire 1 is a low aspect tire comprising a pair of
bead parts 3 each having a bead core 2, side wall parts 4 extending
from the bead parts 3 outwardly in the radial direction of tire,
and a tread part 5 for linking between their outer ends, and in the
case of the tire shown in FIG. 1, the aspect ratio H/SW of the tire
sectional height H to the tire width SW is set at 0.62.
Between the bead parts 3, 3, a carcass 7 is straddling, of which
both ends of the main body part 7A extending through the tread part
5 and side wall parts 4 are folded back from inside to outside
around the bead core 2, and a belt layer 9 is provided on the
carcass 7 and radially inward of the tread part 5.
The carcass 7 is composed of, in this embodiment, two carcass plies
7a, 7b having carcass cords, which are made of organic fiber cords
such as nylon, polyester and aromatic polyamide, arranged at an
angle of 70 to 90 deg. with respect to the tire equator CO. And the
inside carcass ply 7a covers the folding end 7b1 of the outside
carcass ply 7b, and folding end 7a1 of the inside carcass ply 7a is
terminated near the maximum width position of the tire in the
standard internal pressure state. Between the main body part 7A of
the carcass 7 and the folding part 7B, there is a bead apex 10
extending radially from the bead core 7a in a taper form in the
tire radial direction, which is made of hard rubber with JISA
hardness of 65 to 90 degrees, thereby enhancing the tire lateral
rigidity, together with the high turn up structure of the carcass
7.
The bead part 3 comprises known reinforcing structures including,
for example, a bead filler for reinforcing the bead apex 10
together with the bead core 2, and a rim dislocation preventive
chafer.
The belt layer 9 is, in this embodiment, of two-ply structure
consisting of an inside belt ply 9a adjacent to the outside of the
carcass 7 and its outside belt ply 9b. And the belt layer 9 along
the carcass 7 has the belt width BW broader than the tire ground
contact width TW so as to reinforce the tread part 5 almost over
its entire width by its hoop effect. The tire ground contact width
TW mentioned herein refers to the linear length between the ground
contact outer edge points E, E which are points on the outer edge
of the tire axial direction of the tread ground contact surface TS
in the standard load state having the tire mounted on the standard
rim 8, inflated with standard internal pressure, and loaded with a
standard load. And the belt width BW is the linear length between
the belt outer edges U, U which are axial outer edges of the belt
layer where least two belt plies overlap, in the same standard
internal pressure state.
The belt width BW should be preferably in a range from 0.7 to 0.85
times or less of the tire width SW. More specifically, if less than
0.7 times, it results in an insufficient restraint force on the
carcass 7, especially the restraint force on the overhang part of
the carcass 7 projecting from the bead part 3 to outside in the
tire axial direction along with the promotion of depression. This
shortage of restraint force makes the ground contact pressure
uneven in this area as the outside diameter is increases in the
radial direction of the tire in the shoulder part due to the
centrifugal force and tire internal pressure along with high speed
revolution.
If exceeding 0.85 times, to the contrary, the tire rigidity is
excessively heightened and the riding comfort becomes poor.
Therefore, the belt width BW should be preferably 0.75 to 0.85
times the tire width SW.
The belt plies 9a, 9b are composed of belt cords inclining at an
angle of 10 to 30 deg. with respect to the tire circumferential
direction, respectively. And the belt cords are made of high
modulus cords with the initial tensile elasticity of about 2500
kg/cm.sup.2 or higher, for example, organic fiber cords such as
aromatic polyamide fibers and carbon fibers, or inorganic fiber
cords such as metal fibers and glass fibers, and steel cords are
used in this embodiment. Depending on requirements, cords of
different materials may be used for each belt plies 9a and 9b. At
the end of the belt layer 9, a soft breaker cushion 13 is placed
against the carcass to alleviate the stress.
Radially outside the belt layer 9, a reinforcing band 15, which is
made of organic fiber cord of relatively high strength and low
mass, such as nylon cord in this embodiment, is provided so as to
suppress the lifting of the belt layer 9 due to centrifugal force,
etc. Meanwhile, the reinforcing band 15 is composed of a first band
ply 15a which covers the outer end of the belt ply 9b to prevent
separation from the outer end, and a second band ply 15b which
cover the entire width of the belt layer 9 together with the first
band ply 15a to improve the tread stiffness uniformly.
In the outside tread surface S of the tread part 5, a pair of main
circumferential grooves 16 for dividing the tread surface S into a
crown part S1 including the tire equator CO and its outer shoulder
parts S2 are disposed. The grooves 16 extend linearly in the tire
circumferential direction and through near the intersection H of
the first arc P1 and second arc P2 forming the specific curvature
plane P of the tread surface S.
The specific curvature plane P comprises, as shown in FIG. 4, a
first arc P1, a second arc P2 and a third arc P3.
The first arc P1 has the radius R1 of curvature of which center is
on the tire's equatorial plane and passes through the tire's
equatorial point A. The second arc P2 has the radius R2 of
curvature of which center is on the tire's equatorial plane and
intersects with the first arc P1 at the intersection H distant from
the tire's equatorial plane by 0.2 to 0.25 times the tire width
SW.
The third arc P3 has the radius R3 of curvature of which the center
is on the normal line (n) set up on the tread surface S at the
ground contact outer edge point E, and passes through the belt
intermediate height point F and the ground contact outer edge point
E. The belt intermediate height point F is the point at which a
tire axial direction line L extending parallel to the tire axis
from the thickness center of the belt layer 9 at the axial outer
edge U of the belt layer crosses the tread surface S. And this
third arc P3 is smoothly contiguous to the second arc P2 through
its coupling line P2a.
In this specification, meanwhile, the tire outer surface between
said belt intermediate height points F, F is called the tread
surface S.
The main circumferential grooves 16 extend, as shown in FIG. 2, in
the tire circumferential direction near the intersection H of the
first arc P1 and second arc P2. And in the crown part S1 and in the
shoulder part S2, lateral grooves 19 intersecting with the main
circumferential grooves 16 are disposed with specific intervals,
whereby the parts S1 and S2 are divided into multiple blocks. The
lateral grooves 19, in this embodiment, has narrow width 19W and
geometrically folded shape.
And also, in this embodiment, in the crown part S1, there is at
least one subsidiary circumferential groove 20 extending in the
tire circumferential direction approximately parallel to the main
circumferential grooves 16. Incidentally, the subsidiary
circumferential grooves 20 may be also disposed in the shoulder
part S2, or may be in both crown part S1 and shoulder part S2.
The main circumferential grooves 16 and subsidiary circumferential
grooves 20 are straight grooves in this embodiment, and the groove
width 16W of the main circumferential grooves 16 is broadly formed
0.06 to 0.10 times the tire width SW. As a result, the water
draining effect may be enhanced while decreasing the drop of
cornering force. If the groove width 16W is less than 0.06 times
the tire width SW, the brake performance on the wet road is
insufficient, and if exceeding 0.10 times, rail wear or other
uneven wear is encourage near the groove edge.
Meanwhile, the area "near the intersection H" is the length not
more than 1/2 of the main circumferential groove width 16W, that
is, the range in which the opening off the main circumferential
grooves 16 can pass through the intersection H.
The subsidiary circumferential grooves 20 are designed to enhance
the gripping performance in cornering and to keep steering
stability. And for suppressing the pattern noise by relaxing the
road surface impact noise of blocks, the groove width 20W is set at
0.1 to 0.3 times the groove width 16W of the main circumferential
grooves 16. If less than 0.1 times, the water draining performance
is insufficient. If exceeding 0.3 times, the pattern rigidity in
the widthwise direction is decreased, thereby lowering the steering
wheel response and breakaway controllability.
The number of subsidiary circumferential grooves should be
preferably one to four, and in addition to the main circumferential
grooves 19, lateral grooves 19 and subsidiary circumferential
grooves 20, the tread pattern may be altered in various manners,
for example, by disposing sipes and lug grooves.
Concerning the radius R1, R2 of curvature, in this embodiment in
which the aspect rate H/SW is 0.62, the radius ratio R1/R2 is
determined in a range from 1.6 to less than 2.6, and the radius
ratio R2/R3 is in a range from 4 to 12, among the radius R1, R2, R3
of curvature of the specific curvature plane P.
This specific curvature plane P found by the inventors is an ideal
curved surface capable of enhancing the steering stability from the
viewpoint of ground contact surface shape. That is, by employing
the specific curvature plane P, such a ground contact surface TS as
the shapes d1, d2 shown in Fig. 5(a), (b), which is an
approximately oblong rectangular shape wherein the ground contact
front and rear edges e1, e2 are nearly parallel to the tire axis,
can be obtained. As a result, an even ground contact pressure
distribution and a high cornering force are obtained, and the
steering wheel response and gripping performance when running
straightly or at the beginning of turning are enhanced.
If the radius ratio R1/R2 is less than 1.6, as shown in FIG. 5(c),
the ground contact length of the crown part S1 is longer than the
ground contact length of the shoulder part S2, and the ground
contact front and rear edges e1, e2 become curves, so that an
irregular wing-shaped ground contact surface shape d3 is formed,
which is inferior in the ground contact performance. If the radius
ratio R1/R2 is 2.6 or more, as shown in FIG. 5 (d), (e), the ground
contact length of the crown part S1 becomes very long and
irregular, nearly rhombic ground contact shapes d4, d5 are formed,
and the ground contact performance is nonuniform, and the cornering
force is lowered.
Furthermore, in the specific curvature plane P, the radius rative
R2/R3 of the second arc P2 and third arc P3 is determined in a
range of 4 to 12. Therefore, when cornering, the third arc P3 which
is outside the ground contact outer edge point E can be newly set
on the ground, as shown in FIG. 6, as compared with the ground
contact surface shape d6 in prior art. As the result, the decrease
of ground contact width and increase of ground contact length are
suppressed, so that the cornering force may be optimized.
According to FIG. 7(a), (b) showing the relationship of the radius
ratio R2/R3 and ground contact width decrement and the breakaway
controllability, so longas the radius ratio R2/R3 is in a range of
12 or less, especially 10 or less, the decrease of ground contact
width can be suppressed, and the cornering force can be heightened,
so that the breakaway controllability is enhanced. However, if the
radius ratio R2/R3 is less than 4, the uneven wear resistance is
lowered, and therefore the radius ratio R2/R3 is in a range of 4 to
12, or more preferably 6 to 10. FIG. 7(a) shows the measurement
when the slip angle is 5 degrees, and the broken line indicates the
conventional level. FIG. 7(b) shows the result of evaluation of
breakaway controllability by actual vehicle feeling test, and the
broken line refers to the conventional tire.
In order to effectively exhibit the characteristics of this
specific curvature plane P, as shown in FIG. 3, it is necessary to
keep the tread surface S in contact with the specific curvature
plane P, at least in a range Q1 of the length of 30% of the tire
width SW around the tire's equator CO, a range Q2 distant from the
tire's equator in a range of 37.5% to 45% of the tire ground
contact width TW, and a range Q3 between the ground contact outer
edge point E and the belt intermediate height point F. In this
example, meanwhile, the main circumferential grooves 16 are
disposed between the range Q1 and the range Q2, and a nearly smooth
curvature surface is contiguous, including the spacing between the
range Q2 and the range Q3. As a result, the tread surface S having
nearly the same high steering stability performance as the specific
curvature plane P is obtained. Meanwhile, the other regions than
the ranges Q1, Q2, Q3 may be Further set along the specific
curvature plane P, or the entire surface of the tread may be formed
along the specific curvature plane P.
In the relation between the aspect rate H/SW and the radius ratio
R1/R2, when the aspect rate H/SW is 0.55 or less, the ratio R1/R2
in a range from 2.6 to 4.6, when the aspect rate H/SW is in a range
from more than 0.55 to less than 0.70, the ratio R1/R2 is in a
range from 1.6 to less than 2.6, and when the aspect rate H/SW is
0.7 or more, the ratio R1/R2 is in a range from 1.2 less than 1.6.
And in this relation, then the slip angle is zero degrees, it is
found that the ground contact surface shape can be optimized same
as in Fig. 5(a), (b) by the inventors.
This is because the deflection when the tire contacts with the
ground is larger as the aspect rate H/SW of the tire is larger,
that is, the tire sectional height H is larger, and therefore by
setting the radius R2 of curvature closer to the radius R1 of
curvature, the ground contact surface of an oblong rectangular
shape with the ground contact front and rear edges approximately
parallel to the tire axis may be obtained.
EXAMPLE
A tire having a structure as shown in FIG. 1 and with the size of
225/50R16 conforming to the specification in Table 1 was
experimentally manufactured, and the steering stability of this
tire was tested by actually driving the vehicle on both dry road
surface and wet road surface to evaluate it. The results of
evaluation are given in Table 1 in the five-point scoring system,
in which the higher score means the higher evaluation.
Incidentally, even if the tire employing the above mentioned
specific plane P has not the main grooves 16 near the intersection
H, the optimal ground contact surface can be obtained, the limit
performance on the dry road can be enhanced.
The invention being thus described, it will be obvious that the
same may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the invention,
and all such modifications as would be obvious to one skilled in
the art are intended to be included within the scope of the
following claims.
TABLE 1
__________________________________________________________________________
embodiments comparisons 1 2 1 2 3
__________________________________________________________________________
radius ratio R1/R2 4.3 3.0 8.5 3.8 1.7 radius ratio R2/R3 8.3 7.5
17.0 13.5 18.2 main groove shape linear No. of grooves 2 2 2 none 2
groove width* 0.09 0.07 0.05 -- 0.13 lateral groove groove width**
0.25 0.25 0.25 0.25 0.25 subsidiary shape linear groove No. of
grooves 1 1 none 1 1 position crown crown -- crown shoulder groove
width** 0.2 0.2 -- 0.1 0.1 steering stability on dry road 3.2 3.5
2.6 3.0 2.7 steering stability on wet road 3.4 3.3 3.0 2.5 2.5
__________________________________________________________________________
*The groove width is expressed as the ratio to the tire width.
**The groove width is expressed as the ratio to the main groove
width.
* * * * *